The principle straightness error of cutting square in work-pieces can be controlled by choosing a suitable pitch diameter of the planetary gear in the machine tools. 选取适当的车头行星轮的分度圆直径，可以有效地控制车方原理的直线度误差。
The evolutional model and the calculation process are introduced in detail.The flatness error is discussed as an example. 文中以平面度误差为例，详细地介绍了进化模型的建立及计算方法。
